A hermetic compressor is generally formed to have, for example, a compression mechanism of a reciprocating type, a rotary type or a scroll type inside a hermetic container. The compression mechanism sucks in, compresses and discharges a refrigerant. The suction, compression and discharge of the refrigerant cause pulsation, so that vibration having a low frequency of 50/60 Hz attributed to operating rotational speed and noise are transmitted via the refrigerant and lubricating oil inside the hermetic container. At the same time, harsh harmonic noise in a human audible range, such as suction/discharge valve tapping noise of the compression mechanism, is transmitted to the hermetic container through a solid contact portion for excitation, thereby producing noise.
In particular, the hermetic compressor of the reciprocating type has the compression mechanism suspended inside the hermetic container by suspension springs, and the hermetic container has a large inside diameter. Thus, the hermetic container has low rigidity and also has a low natural frequency. For this reason, the harmonic noise in a range of about 2 kHz to 8 kHz, such as the valve tapping noise produced from the compression mechanism of the hermetic compressor, overlaps readily with the natural frequency of the hermetic container that is determined by, for example, a shape, a plate thickness or material of the hermetic container. Consequently, noise levels particularly tend to increase in the above frequency band.
The hermetic compressor of the rotary type or the like has a noise problem associated with a fundamental wave having 50 Hz/60 Hz pressure pulsation. On the other hand, the hermetic compressor of the reciprocating type problematically produces harmonic noise in a band of resonance frequencies (2 kHz to 8 kHz) that is attributed to the natural frequency of the hermetic container, and the resonance frequencies in this band are higher by an order of magnitude or more than the frequency of the problematic noise of the hermetic compressor of the rotary type or the like. This problem is peculiar to the reciprocating type.
As such, conventional hermetic compressors of various types have various noise control measures. One of those measures uses a dynamic vibration absorbing effect (refer to, for example, PTL 1).
FIG. 14 illustrates a hermetic compressor described in PTL 1. This compressor is a hermetic compressor of a reciprocating type. Weight 102 is provided to hermetic container 101. This weight 102 brings a solid frequency of hermetic container 101 into conformity with a natural frequency of legs 103 each formed of a cushioning member for supporting hermetic container 101. Through a dynamic vibration absorbing effect of legs 103, vibration of hermetic container 101 is damped. In this way, noise is reduced.
It is to be noted that inside hermetic container 101, compression mechanism 104 is provided, and suspension springs 105 are provided for suspending compression mechanism 104 inside hermetic container 101.
Another noise control measure uses a vibration damping plate (refer to, for example, PTL 2).
FIG. 15 illustrates hermetic container 201 of a hermetic compressor described in PTL 2. The compressor is provided with vibration damping plate 202 that is in partial contact with an inner wall surface of hermetic container 201 while having elastic force. Through a contact friction damping effect of contact parts of vibration damping plate 202, vibration of hermetic container 201 is damped, whereby noise is reduced.
The hermetic compressor described in PTL 1 has the vibration of hermetic container 101 damped through the dynamic vibration absorbing effect of legs 103, whereby its noise is reduced. However, there are cases where a satisfactory noise control effect is not obtained when the hermetic compressor is mounted to an appliance, such as a refrigerator, in parts that change in rigidity. Thus, there is a problem of lack of reliability.
In other words, legs 103 are parts where the hermetic compressor is mounted and fixed to the appliance, such as the refrigerator, via grommets or fixtures. However, when fixed to the appliance, legs 103 change their rigidity and reduced mass according to, for example, a shape or material of the grommet or the fixture or a fixed state, thereby changing their natural frequency. For this reason, a great deviation is caused between the natural frequency of hermetic container 101 that is modulated by weight 102 and the natural frequency of legs 103. As a result, a satisfactory dynamic vibration damping effect cannot be exerted, so that the hermetic compressor cannot achieve noise reduction or has a small noise reducing effect, thus lacking reliability.
In addition, the above-described hermetic compressor requires weight 102 having relatively large mass and relatively large volume for the purpose of bringing the natural frequency of hermetic container 101 into conformity with the natural frequency of legs 103. Accordingly, the hermetic compressor has an increased parts count and increased weight, thus becoming high-cost and having an increased size. For this reason, there are cases of such an adverse effect that capacity inside the appliance such as the refrigerator reduces as the appliance has increased mounting capacity.
The hermetic compressor described in PTL 2 has vibration damping plate 202 fixed at fixed part 203 to the inner surface of hermetic container 201 by welding, and contact parts 204a, 204b, 204c, 204d, 204e, 204f of vibration damping plate 202 are in elastic contact with hermetic container 201, whereby the contact friction damping effect is obtained in a relatively wide frequency band. However, there are cases where a satisfactory noise control effect is not obtained. Thus, lack of reliability is problematic. In other words, vibration damping plate 202 of this structure makes elastic contact while undergoing plastic deformation when being fixed by welding to hermetic container 201 at fixed part 203, thus involving contact location variations and contact load variations. As a result, the contact friction damping effect of vibration damping plate 202 varies, and the hermetic compressor may possibly have a small noise reducing effect. Thus, this hermetic compressor lacks reliability.